Many wireless communication devices such as cellular phones, smartphones, tablet computers, or other devices use a SIM (subscriber information modules) to store the subscriber's telephone number and other subscriber information, such as contact lists, as well as network information for the subscriber's service provider. Some wireless communication devices permit use of two or more SIMs in the device. A user may use a dual SIM device to make and receive calls or send and receive texts and other data on two different telephone numbers, on two different subscriber accounts, or over two different networks simultaneously. For example, a traveler may retain a SIM in the device for the traveler's home country telephone number, and may install a second SIM into the device for a local telephone number while traveling in a foreign country. The local account SIM may provide service at local rates, particularly for calls within the foreign country, while the home account SIM permits the device to receive calls on the home country number. By contrast, a single SIM device would disable the device for use with the home country number if the SIM were replaced with a SIM for service within the foreign country. In a second example, a user may choose to assign one SIM in the dual SIM device to a business telephone number or account and a second SIM to a personal telephone number or account, so that the user may use the same device for both accounts.
Some wireless communication devices provide dual connectivity wherein the wireless device connects to two eNodeBs (or base stations) using a single user account and a single SIM. Dual connectivity improves data throughput and robustness. The dual connectivity is carried out by a single SIM in the device communicating with two eNodeBs within the same network.
Wireless devices are limited in the amount of power they may use for transmitting or uplinking data. A wireless device that is communicating with an eNodeB (or base station) may report to the eNodeB on the amount of power available for uplinking data from the wireless device to the eNodeB. This report is referred to as a power headroom report (PHR). Upon receiving the power headroom report, the eNodeB may condition the communication channel by allocating resources to the communication link that are appropriate for the reported power, setting data communication rates, setting noise canceling resources, and the like.
The 3GPP standard provides that a power headroom report from a user device to an eNodeB for a first dual connectivity connection may include in the report the power being used for the second dual connectivity connection by that same SIM to the second eNodeB. Both of the eNodeBs are in the same network.